Loudspeakers



July 17, 1962 c. E. WATTS 3,044,576

LOUDSPEAKERS Filed April 2, 1958 2 Sheets-Sheet 1 IN VE N TOR M mum:

A TTOR/VE Y July 17, 1962 c. E. WATTS 3,044,570

LOUDSPEAKERS Filed April 2, 1958 2 Sheets-Sheet 2 /N VEN TOR M5. Mm; 2 1 43.4

ATTORN Y United States Patent Ofiiice 3,044,570 Patented July 17, 1962 3,044,570 LOUDSPEAKERE? Cecil Ernest Watts, Sunbury-on-Thames, England, as-

signor to Cecil E. Watts Limited, Surrey, England, a British company Filed Apr. 2, 1958, Ser. No. 725,823 Claims priority, application Great Britain Apr. 8, 1957 3 Claims. (Cl. 181-31) The present invention relates to loudspeakers.

In the specification ofmy British Patent No. 769,204 there is described a loudspeaker of novel construction and that specification is concerned with reproduction of intermediate and low frequencies.

One of the difficulties met with in reproducing the highest frequencies, and to alesser extent also the intermediate frequencies, arises from the focusing effect of the diaphragm which radiates the sound. It is known that when the dimensions of the diaphragm, or that part thereof which is effective at any frequency, are comparable with the wavelength corresponding to that frequency, interference effects produce a concentration of sound intensity around the axis of the diaphragm.

The original source of all signals which have to be reproduced by a loudspeaker is a microphone. The waveform generated by a microphone contains not only a representation of the sound waves reaching it directly from a source, such as a musical instrument, but also representations of reflections of the sounds from the source from the boundaries of the space in which the source is located. For satisfactory sound reproduction it is, therefore, necessary to convert the signal waveform into sound waves all the frequency components of which are radiated in all directions, or at least over a wide angle.

The present invention has for its principal object to apply these considerations to improving sound reproduction, and, as one important step in such improvement, to reduce the directional efifects at the higher frequencies.

According to the present invention there is provided a loudspeaker comprising two or more separately driven diaphragrns arranged to reproduce different parts of the acoustic frequency range, these diaphragms being disposed at least approximately in axial alignment.

The axis of a diaphragm is a line from its center in the direction of its vibration and axial alignment of the diaphragms therefore means that their axes are coincident.

'I he diaphragms should be arranged to be energized in phase, that is to say in such a manner that in response to a unidirectional transient they move in the same direction, that is, the diaphragms are driven in the same direction in space.

According to a subsidiary feature of the invention the loudspeaker comprises a radiator of the low acoustic frequencies of approximately cylindrical, frusto-conical, or flattened cylindrical or frusto-conical shape, so arranged in relation to the aforesaid diaphragnrs that the axis of the diaphragms passes eccentrically through the said radiator.

The inventlon will be described by Way of example with reference to the accompanying drawing in which FIGURE 1 is a view in sectional elevation of one embodiment of the invention, FIGURE 2 is a plan View in section on the line IIII of FIGURE 1 to a reduced scale.

In the drawing a cabinet has an upper wall 10, a lower wall 11 and joining these walls a wall 12 of flattened frusto-conical shape. The upper part of the cabinet is divided by two vertical transverse walls 13 and 14, a horizontal transverse wall 15 and an inclined wall 16, all these walls extending from front to back of the wall 12.

In the upper wall 10 are formed apertures 17 and 18. In aperture 18 is mounted a first loudspeaker unit 19 having a diaphragm 20 and a driving electromagnet 21.

Three loudspeaker units 22, 23 and 24 of the same construction as the unit 19 but of progressively smaller size are mounted in and over the aperture 17. Thus the unit 22 is mounted in the aperture 17, the unit '23 is supported by brackets 25 above and in axial alignment with the unit 22, and the unit 24 is supported by brackets 26 between and in axial alignment with the units 22 and 23. The diaphragms of units 19, 22 and 24 face upward and that of the unit 23 faces downward.

In one example, the diaphragm of the first unit 19 has a diameter of about 11 inches, that of the second unit 22 a diameter of about 10 inches and an axial height of about 4 inches, the diaphragm of the third unit 23 has a diameter of about 5 inches and an axial height of about 2 inches, and that of the fourth unit 24 a diameter of about 2 inches and an axial height of about 1 inch. The four units are designed to operate over approximately the ranges 30 to 200, 200 to 1000, i000 to 5000, and 5000 upward respectively, and suitable cross-over networks are provided in order to feed to each unit the appropriate part of the frequency range. The mouths of the diaphragms of the second and third units 22 and 23' are spaced apart by about 5 inches, and the mouths of the diaphragms of the third and fourth units 23 and 2d are spaced apart by about 2 /2 inches. A circular baffle 27 about 3% inches in diameter is supported by brackets 28 about 3% inches in front of the mouth of the diaphragm of the first unit 19. Thus it will be noted that the second and third units and the third and fourth units are spaced apart by a distance less than the diameter of the larger, that is the diameter of the second and third units respectively.

Over the upper wall 10 and enclosing the third and fourth units 23, 24, which project above the wall 10, is a cover 29 having honeycomb walls. These walls may be formed of approximately horizontal and vertical slats 30 and 31. The openings may be covered with dust-proof fabric (not shown).

The crossover networks operate to prevent all signals outside a given band from reaching a given units. As is known there is always a slight overlap between the adjacent frequency bands in the outputs of such cross-over networks. Diaphragms reproducing adjacent and overlapping bands of frequencies are driven in such a manner as to be in phase at the frequencies in the overlapping regions, that is, the diaphragms are driven in the same direction in space; the purpose in driving the diaphragms in phase in the overlapping frequency regions is to reduce directional effects by reducing the cancellation of sound waves that occur when diaphragms are driven in opposing phase. The arrangement of the second, third and fourth units 22, 23 and 24 in axial alignment serves to mask sounds of frequencies above the range proper to each of the second and third units. Moreover, the disposition of these diaphragms results in avoidance of focusing eifects.

Although examples of dimensions and spacings for the second, third and fourth units have been given, in practice the spacings are so adjusted that all frequencies within the acoustic range of the loudspeaker are radiated in all directions around, and also through an angle above and below horizontal, at approximately uniform intensity.

The unit 19 is loaded by the chamber 33 between the walls 12 and 14, 15 and 11 and 12 and 16, the crossseotional area of this chamber decreasing in a direction away from the unit 19. The chamber preferably terminates in an aperture 34. The unit 22 is loaded by a chamber 35 between the wall 16 and a further transverse wall 36 and between the wall 36 and the wall 13, this chamber preferably terminating in an aperture 37.

The side wall 12 of the loudspeaker constitutes the 3 main radiator of the lowest frequencies and it is noted that this wall is of approximately flattened frusto-conical shape and that the aligned axes of the second, third and founth diaphragm pass eccentrically through this radiator.

A greater number of apertures or vents 34, 3'7 than shown may be desirable and it has been found that the reproduction of the lowest frequencies can be improved by covering these vents with soft material, such as foam rubber, which may be about /2 inch thick.

I claim:

1. A loudspeaker having three frusto-conical' diaphragms for reproducing low, medium, and high frequencies respectively and of large, medium and small diameter respectively, loading means for said large diameter diaphragm comprising a chamber and partitions in said chamber defining a nearly closed passage of cross-section decreasing in a direction away from said large diameter diaphragm, said chamber having boundaries including an apertured end wall and flexible side walls for radiating said low frequencies, said large and medium-diameter diaphragms being mounted in apertures in said end wall, means supporting said small diameter diaphragm from said end wall substantailly coaxial with and spaced from said medium diameter diaphragm with the concave sides of said small and medium diameter diaphragrns facing one another, and three independently energizable electromagnetie driving means coupled to said three diaphragms respectively.

2. A loudspeaker according to claim 1 comprising within said chamber further partitions defining a further loading passage extend from the convex side of said mediumdiameter diaphragm and having a cross-section decreasing progressively in a direction away from the medium diameter diaphragm.

3. A loudspeaker according to claim 1 comprising a bafiie of diameter substantially smaller than that of said large-diameter diaphragm and means for fixedly supporting said baffle spaced from and on (the concave side of said large-diameter diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS 1,877,294 George Sept. 13, 1932 1,951,692 Evens Mar. 20, 1934 2,034,882 Scribner Mar. 24, 1936 2,043,416 Lueg June 9, 1936 2,049,784 Thomas Aug. 4, 1936 2,114,680 Goldsmith Apr. 19, 1938 2,565,069 Engholm Aug, 21, 1951 2,869,667 Leslie Jan. 20, 1959 2,969,848 Farwell Jan. 31, 1961 

